Electric measuring instrument



April 7, 1942- R. MODLINGER ,279, 5

ELECTRIC MEASURING INSTRUMENT Filed Oct. 21, 1938 e+7r F 54-; s/mac i=1,s/lv -al --2/ 30 0/20 b((o/vmcr\s0P/W L 22 a fl n/mar: (10::

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Patented Apr. 7, 1942 ELECTRIC MEASURING INSTRUMENT Richard Modlinger,Berlin, Germany, assignor to General Electric Company, a corporation ofNew York Application October 21, 1938, Serial No. 236,358 In GermanyOctober 22, 1937 7 Claims.

This invention relates to instruments for indicating and measuringalternating current quantitles and particularly alternating currentquantitles such as phase displacement, power-factor, voltage componentsand the like.

It is an object of the invention to provide an improved device formeasuring phase angles of alternating current voltages or currents.

Another object of the invention is the employment of apparatus includinga permanent magnet moving-coil type electric instrument by means ofwhich the phase angle between two electrical quantities may be readdirectly in degrees.

Another object of the invention is the provision of such an instrumentwhich is adapted to measure the power-factor of an alternating currentload.

Still another object of the invention is the employment of such aninstrument for measuring the in-phase component of the voltage in analternating current circuit.

A further object of the invention is the provision of an electricmeter'for indicating and measuring phase displacement and power-factorof alternating current quantities which is independent of voltagefluctuations.

Other and further objects and advantages of the invention will becomeapparent as the description proceeds.

In carrying my invention into effect, I connect an electric meter acrossthe circuit being investigated, the meter being of the dArsonvalgalvanometer type which is capable of responding to only average valuesof voltage or current applied to its terminals. Means are provided forperiodically deenergizing or removing the meter from the circuit for apredetermined period of time during each cycle of the current at a pointin the voltage wave determined by the phase displacement between thecurrent and voltage. I have discovered that the average value of theportion of the voltage wave measured for such predetermined time is afunction of the poweriactor of the circuit and that a meter adapted torespond correctly in proportion to this average value may be calibratedto read the power-factor on a uniform scale or phase displacementbetween the current and voltage on a non-uniform scale and, undercertain conditions, the inphase component of the voltage.

In carrying out my invention in another form I combine two instrumentsof the deflecting type, following different laws expressing therelationship between the torque and current, by mechanically connectingtheir moving elements in such a manner that their effects are opposed.For

example, I may provide one unit in which the torque is directlyproportional to the average value of the current flowing in themetercoil such as a d'Arsonval galvanometer, and a second unit in whichthe torque is proportional to the product of the average value of thecurrent in the meter coil times the cosine of the angle of rotation ofthe meter. Such a device makes possible the direct reading of the angleof phase displacement on a uniform scale and is independent of voltagefluctuations.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and the features whichI believe to be novel and patentable are pointed out in the appendedclaims.

Referring to the accompanying drawing, Fig. 1 represents typical sinewaves of voltage and current, the characteristics of which are beinginvestigated; Fig. 2 illustrates apparatus for measuring thepower-factor or phase angle of a given load when a constant voltage isapplied to the meter or which may be calibrated to measure the in-phasecomponent of voltage when connected to a variable voltage circuit; Fig.2A is a modification of Fig. 2; and Fig. 3 illustrates a modified formof apparatus for giving a correct measurement and indication of thepower-factor or phase angle between two electrical quantities regardlessof voltage fluctuations.

In Fig. 1 a voltage wave is shown following the equation e=Eo sin a,where e is the instantaneous value of the voltage and E0 is the maximumvalue. The current wave having an instantaneous value 1 is shown laggingthe voltage by an angle of 0 degrees. For purposes of illustration,assume that a meter which responds to average values is connected incircuit across the voltage e=Eu sin a at the instant a where the currentwave passes through zero in a positive direction and that the meter isdeenergized or removed from the circuit at the instant b after thecurrent wave has completed one-half cycle. For a given angular phasedisplacement of 0 degrees, there will be a corresponding reading on themeter which is proportional to the average value of the voltage measuredduring the time interval or period ab. This average value (Eab) is equalto the area of the cross-hatched portion of the voltage wave shown inFig. 1, divided by its base and may be stated as cos 0 or Eab=k E cos 9(1) voltage being investigated. This equation aphaving contacts 25.

plies only for the case where the contacts are Equation 1 thus showsthat the average value I of the voltage under the above conditions isproportional to the power-factor (cos of the circult so longas the R. M.S. value of thecircuit voltage remains constant; On the other hand E cos0 represents the in phase component of the voltage and may be useful inmeasuring the power in an alternating current circuit.

The arrangement shown in Fig. 2 is illustrative of one form of apparatuswhich I have devised for carrying out my invention. A load 29 havin apower-factor (cos 0) is connected to an alternating current source 2|,with a voltage represented by the equation e=Eo sin a. In the loadcircuit is placed a series resistor 22 and across this resistor isconnected the operating coil 23 of a vibrator or velectro-mechanicalinterrupter 24 The vibrator armature carrying one of the. relativelymovable contacts 25 is so adjusted and proportioned that it is caused tooscillate or vibrate periodically in synchronism with the currentflowing in, the load circuit and, for the case illustrated in Fig. 1,the vibrator is adjusted so thatits contacts 25 close periodically atthe instant a when the current wave is passing through zero in-apositive direction and open periodically at the instant b, r radianslater in time phase, after the current has completed a half cycle and ispassing through zero in a negative direction.

The meter 29 is of the conventional dArsonval galvanometer typeemploying element 26', as

shown in detail Fig. 3, and a helical spring (not 7 shown) to provide adirectional force or countertorque to the meter shaft. Element 26'includes a permanentmagnet 21 having arcuate pole faces 28, and a movingcoil 29 wound about'a soft iron core 90 mounted for rotation on a shaft9| which operates a pointer 32 cooperating with a scale 33. The coil .29is shown connected in series with the contacts 25 across the load 29.Obviously, instead of connecting the contacts 25 in series with themeter coil 29, I may employ ameter circuit including an externalresistance and connect the contacts 25 in shunt with the meter coil 29,as illustrated in Fig. 2A. With such an arrangement the contacts 29would be adjusted to open at .a and close at b to operatively connectthe meter in the circuit. Inasmuch as the meter 26 is in circuit duringthe period ab, corresponding to 180 electrical degrees or acompletepositive or negativehalf cycle of the current .wave,

i=1. sin (is-0) where I. is the average value of the current flowing inthe meter coil 29. Since the current; flowing in the meter coil 29 isproportional to the voltage of the circuit, Equation 2 may be restatedas Tm laEah (3) From Equations 1 and 3the meter torque Tm may also berepresented by the equation Tm=k4E cos 0 I (4) The helical spring in ameter such as 26 exerts a directional force or counter-torqueproportional to the angle of twist or where T: is the counter-torque, pis the angle of twist, and its is the spring constant. For equilibriumconditions the meter torque and the spring torque must balance, ThusTi=Tm. It follows that ksp=k4E cos 0 or p=ksE cos '0 (6) ing to thevarious power-factors may be read on a non-uniform scale. It may also beobserved :that the expression E cos 0 in Equation 6 is the in-phasecomponent of the voltage of the source 2i applied to the circuit. Themeter may also be calibrated to read this quantity regardless offluctuations in voltage.

f To provide measuring apparatus which will accurately indicate thepower-factor or phase displacement between the current and voltageregardless of fluctuations in voltage of the source 2|, I have devisedthe arrangement disclosed in Fig. 3. I employ an element 26' which isidentical a moving coil ltmounted for rotation on the shaft 3| with theother coil 29. The coil 39 is connected to the load circuit 20 through ahalfwave rectifier "of the copper oxide type or the equivalent. A fullwave rectifier may be used if desired. The moving coils 29 and 38 are soconnected that the torques tending to produce rotation of the pointeroperating shaft 3| are in opposition as indicated by the arrows 40 and4|.

In theelement 35, the direction of the field 39. the conductor 38, andthe direction of the force are no longer mutually perpendicular to oneanother, as obtains in element 26'. due to the rectillnear field 39.With this arrangement, when the coil 38 is turned through an angle aboutthe axis of rotation in the rectilinear field 29 the component or, onemay say, the intensity of the field producingtorque is no longerconstant throughout the angular range of the instrument, but varies inaccordance with the cosine of the angle through which the coil 39rotates. Thus the counter-torque produced by the second element 2! isTc=kcluwgi 008 P, where I(avg) 18 the average value of the currentflowing in the meter coil. This current is proportional to the voltageapplied to the coil 39 so that the torque may be expressed asTc=klE(cvc) 605 p (7) where Emn is the average value of the voltagerectified by the rectifier 42 and p is the angle of rotation of themeter. Equation 7 may be stated in terms of the efiective or R. M. S.voltage applied to the load or Again for equilibrium conditions, Tc=Tm.Equating (4) and (8) gives kioE cos p=k4E cos 0,

p=ki10 9) From Equation 9 it may be observed that the angular deflectionof the meter is directly proportional to the phase angle between theelectrical quantities being investigated so that the statutes, I havedescribed the principle of operation of my invention together with theapparatus which I now consider to be the best embodiment thereof, but I'desire it to be understood that the apparatus shown is only illustrativeand that the invention may be carried out by other means. For example,my arrangement is not limited to the use of a vibrating relay fordeenergizing the electric meter during a portion of the cycle butincludes any equivalent arrangement which will operate in synchronismwith the current impulses to deenergize the meter at the desired time.As indicated previously, my invention also contemplates arrangementswherein the meter tenninals are short-circuited instead of opening themeter circuit.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a device for measuring and indicating the power-factor of aconstant voltage altemating current circuit, a meter, and meansincluding an electroresponsive device operative periodically insynchronism with the current in said circuit for operatively connectingthe meter to the voltage of said circuit only during half-cycles of thecurrent which are of one polarity.

2. An in phase voltage measuring device, an alternating current circuit,a meter adapted to be supplied with current proportional to the voltageof said circuit, and an electroresponsive device responsive to thereversals of the current flowing in said circuit for causing the voltagesupplied to said meter to be proportional also to the component thereofwhich is in phase with the current of said circuit.

3. In an in phase voltage measuring device, an alternating currentcircuit, a meter adapted to be supplied with current proportional to thevoltage of said circuit, and an electromagnetic vibrator havingelectrical contacts adapted to vibrate periodically in synchronism withthe current in said circuit for opening the meter circuit when thecurrent is of one polarity and closing the meter circuit when thecurrent is of the opposite polarity.

4. In an instrument responsive to the phase displacement between twoalternating current quantities, in combination a shaft adapted forrotation, means for producing a radial magnetic field of constantstrength including spaced pole .the product of the average value of saidunidirectional voltage times the cosine of the angle of rotation of saidshaft, whereby the reading of said instrument is made independent ofvariations in the magnitude of said first alternating current quantity.

5. In an instrument responsive to the phase displacement between twoalternating current quantities, in combination a shaft adapted forrotation, means for producing a radial magnetic field of constantstrength including spaced pole pieces having arcuate faces, an electriccoil mounted on said shaft for rotation between said pole faces, meansfor operatively connecting said coil to a first alternating currentquantity during like polarity half-cycle portions of each cycle of asecond alternating current quantity, means for producing a rectilinearmagnetic field of constant strength including spaced pole pieces havingplane faces, a second electric coil mounted on said shaft for rotationbetween said planefaced pole pieces, and means including a rectifier forconnecting said second coil to said first electrical quantity, wherebythe reading of said instrument is made independent of variations in themagnitude of said first alternating current quantity.

6. In combination with an alternating current circuit, apparatusresponsive to the component of the voltage of said circuit which is inphase with the current thereof comprising an electrical measuringinstrument, connections for energizing said instrument in response tothe voltage of said circuit, circuit opening and closing meansassociated with said connections, and means responsive to the reversalsof the current flowing in said circuit for operating said circuitopening and closing means to energize said instrument only when thecurrent flowing in said circuit is of a given polarity.

7. In combination with an alternating current circuit, an electricalmeasuring instrument, connections for energizing said instrument inresponse to the voltage of said circuit, circuit opening and closingmeans associated with said connections, means responsive to thereversals of the current flowing in said circuit for operating saidcircuit opening and closing means to energize said instrument only whenthe current flowing in the circuit is of a given polarity, saidinstrument to have a torque proportional to the component of voltage inphase with the current, and means energized in response to the voltageof said circuit for producing a counter torque on said instrument ofsuch character as to cause its deflection to be independent of changesin voltage and proportional to power factor.

RICHARD MODLDIGER.

